Select the best definition of Primary open-angle glaucoma.

A. Separation of the neurosensory retina from the underlying retinal pigment epithelium. B. Acute retinal ischaemia causing sudden painless monocular visual loss. C. A chronic optic neuropathy often associated with raised intraocular pressure and open drainage angles. D. Sudden closure of the anterior chamber angle causing painful red eye and raised intraocular pressure.